Conventionally, photoreceiving elements such as solid stat image forming elements have generally been enclosed in ceramic packages in such a manner as to result in some spaces between the elements and the packages, to produce photosemiconductor devices. These ceramic packages, however, are undesirable because the constituent materials therefor are relatively expensive and large-scale production thereof is inefficient. Therefore, resin moldings for plastic packages have been studied. Of such resin molding techniques, molding with epoxy resin compositions in particular have been extensively studied. Such epoxy resin compositions are obtained by melt-mixing epoxy resins, hardeners, curing accelerators and other additives with heating.
However, the thus-obtained epoxy resin compositions for use in the molding of photosemiconductors are undesirable because the dispersion of each of the epoxy resin, hardener, and curing accelerator is insufficient so that these components have not been mixed uniformly at the molecular level. For this reason, if transfer molding, for example, is carried out using such an epoxy resin composition for photosemiconductor molding, the following problems result.
In producing this resin molding, when the epoxy resin composition for photosemiconductor molding is cured, the curing reaction proceeds at higher rates in some parts and at lower rates in other parts because the dispersion of each component in the epoxy resin composition is not uniform when viewed on a molecular level. Such uneven rates of the curing reaction result in unevenness in the density of the cured molding resin, and this causes the refractive index of the molding resin to vary over a wide range. The molding resin has optical unevenness which appear as a striped pattern extending in the direction of the resin flow. If, for example, an area sensor of a solid state image forming element is molded with a conventional epoxy resin composition for photosemiconductor molding by the method described above and intense parallel light rays are allowed to strike upon the molded area sensor with an iris diaphragm having f-32, such optical unevenness in the molding resin as above causes the resulting image to have a striped pattern.